Don't always fully repaint on viewport resize

Source/core/rendering/RenderView.h

Index: Source/core/rendering/RenderView.h
diff --git a/Source/core/rendering/RenderView.h b/Source/core/rendering/RenderView.h
index 9036758c14ab17312d6cd796826c0ea52bfbd8c0..d439b84be1b5234a4f3d8cbfe570f444989d9fd4 100644
--- a/Source/core/rendering/RenderView.h
+++ b/Source/core/rendering/RenderView.h
@@ -123,6 +123,7 @@ public:
     }
 #endif
 
+    bool shouldDoFullRepaintForNextLayout() const;
     bool doingFullRepaint() const { return m_frameView->needsFullRepaint(); }
 
     // Subtree push
@@ -242,6 +243,8 @@ private:
 
     bool shouldUsePrintingLayout() const;
 
+    RenderObject* backgroundRenderer() const;
+
     FrameView* m_frameView;
 
     RenderObject* m_selectionStart;